Atmospheric Angular Momentum Contibutes to U.S. (and Elsewhere) High Wind Events

+AAM Causes High Wind Events
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01/29/2019, 3:07 pm EDT
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Strong positive phase of atmospheric angular momentum leads to unusually destructive wind events across U.S.

Fig. 1:  Ahead of an arctic air mass blizzard warnings (red) and winter storm warnings (purple) are issued by NOAA with following wind chill into northern Minnesota (light blue). On the back side of this cold event a high wind warning is issued for wind gust potential to 80 mph centered on South Dakota to Nebraska tonight and Monday. The high wind is made more intense by a strong positive phase of atmospheric angular momentum.

Discussion: A high wind warning is issued by NOAA for the northwest to central Great Plains (Fig. 1) in anticipation of strong northwest wind aloft on the back side of strong upper trough funneling in-between the developing storm and height of the Rocky Mountains to cause wind gusts reaching 80 mph arriving late tonight and Monday (Fig. 2).  The unusually strong wind aloft driving this event is similar to the set-up propelling unexpected excessive wind (gust to 81 mph in Blue Hill, Mass.) in New England late last week.

Unique to these high wind events is the presence of strong positive phase of global atmospheric angular momentum (+AAM) forecast by all models (Fig. 3) in the +2 to +2.5 range the next 14 days (and much stronger values by the American operational models for early February). The +AAM forecast of +2.0 to +2.5 already represents about +4 to +5 St Dev therefore a very intense signature.

+AAM regimes represent stronger-than-normal westerly flow aloft in the middle latitudes. Research has shown that there is a relationship between +AAM events and presence of El Nino (warm Nino34 SSTA) and/or strong Madden Julian oscillation (MJO) events in the equatorial Pacific Ocean.  The Nino34 SSTA is in a marginally warm El Nino signature now while strengthening MJO in the equatorial West Pacific is forecast by all models.

Given the 2-week (and beyond) extreme +AAM forecast additional severe wind episodes will occur across the U.S. Focusing on the most extreme through the next week or so the next event is forecast across Chicago to Detroit next Saturday night. 850 MB wind forecasts support potential for near hurricane force wind gusts in these locations (Fig. 4). The events shifts east to New York/New England next Sunday and is slightly weaker but still supporting wind gusts to 60 mph (Fig. 5).

Models vary but at least 2 more excessive wind events (approaching hurricane force in gusts) focused on the Northeast Corridor Feb. 7-8 and East-Central U.S. Feb. 11-12 are indicated by the GFS. Until the +AAM regime calms down there will be additional unusually high wind episodes of particular importance to electricity distribution. Other high population northern hemisphere locations are also affected such as U.K. (today), France (Tuesday night) and Spain plus the Baltic nations late this week.

Fig. 2: Strong 850 MB wind (5,000 feet) across South Dakota/Nebraska will cause hurricane force wind gusts tonight/Monday.

Fig. 3: Atmospheric angular momentum 14-day forecast by all models.

Fig. 4: Strong 850 MB wind (5,000 feet) across Chicago to Detroit will cause hurricane force wind gusts next Saturday night.


Fig. 5: Strong 850 MB wind (5,000 feet) across NY/New England will cause wind gusts to 60-65 mph next Sunday.